1. Field of the Invention
This invention relates to surgical sutures and in particular to a surgical suture with a treated end for insertion into a surgical needle, and a treatment method therefor.
2. Background of the Art
Surgeons often use needles with attached sutures in surgical operations. A typical suture-needle combination is shown in FIG. 1. Generally, such needle suture combinations comprise a non-eyed needle with a cylindrical hole in a barrel shaped rear end for receiving a suture, and a suture with a treated end which is received into the hole. Provided with a needle suture combination, operating room personnel need not waste time trying to thread an eyed needle with a suture. After using the needle-suture combination to close a wound the surgeon may detach the needle either by cutting the suture or by pulling on the needle with sufficient force to detach the needle from the suture.
In making suture needle combinations, whether the needles be eyed or non-eyed, it is generally necessary to treat the tip of the suture in some manner in order to make it easier to insert the tip into the barrel end of the needle. Braided or woven sutures especially have a tendency to "broom" or flare out at the ends. The purpose of the treatment is to stiffen the tip of the suture, as, for example, the end of a sewing thread is wetted and twisted so that it may be inserted into the eye of a sewing needle.
With regard to surgical sutures, this "tipping" process generally has been accomplished by coating and/or soaking the end of the suture with a solution of a resinous tipping solution. One such solution is Mariotte mixture, which comprises a solution of polyamide resin in isopropyl alcohol and water. Another such solution is Gould mixture, which comprises a solution of polyamide resin in methanol.
Generally a suture to be tipped is first placed under tension to reduce slack so that it may be maintained in a predetermined position on a drum or other suture holding device. Optionally, the tension may be such as to reduce the diameter of the suture. The suture is then dipped into the tipping solution and allowed to dry while under tension. The sutures are then warmed in a drying oven at about 225.degree. F. for about 10 minutes to dry the sutures. After drying the sutures can be cut and released from tension. The process results in a tipped end on each side of a cut. In cases where tension has optionally been employed to reduce the suture diameter, release of said tension will allow the suture to expand to its original diameter except at the tipped end portion. This can facilitate insertion of the end into a needle. A method for making a needle suture combination wherein the suture end has been treated with resin solutions is described in U.S. Pat. Nos. 3,980,177 and 3,890,975.
Although dipped sutures prepared in accordance with the above procedures have been used successfully, there are several drawbacks with the use of tipping solutions. The main problems are those of consistency and controllability. Non-uniform solvent evaporation, caused by variations in oven temperature and heating time, result in uneven diameter reduction and inconsistency of tipping. Furthermore, the dried residue of polymer left after evaporation can flake off or develop cracks.
A further drawback in these known procedures is that the suture is permanently altered. After the suture has been inserted into a needle there is no need for it to be stiffened. A limp suture will lay in the position in which the surgeon leaves it, whereas a stiff suture can interfere with the suturing operation. Nevertheless, a suture tipped by the prior art solutions will always have a portion containing the stiff residue of included polymer resin.
Heating of certain filaments is known in the art. A method for heat setting of stretch oriented polyglycolic acid filaments is disclosed in U.S. Patent No. 3,422,181. This patent discloses a method for improving the strength retention and absorption rate of a polyglycolic acid filament to be used in a suture by subjecting the filament to dry heat at a relative humidity of not greater than 20% and at a temperature of between 50.degree. C. and 190.degree. C.
Another method which has been employed for treating sutures involves melt fusion, as described in U.S. Pat. No. 4,832,025, issued to Coates. The suture is heated to a temperature at least high enough to "melt fuse" a portion of the outer filaments of the suture. Such temperature is typically about 260.degree. C. to 300.degree. C. (500.degree. F. to 572.degree. F.). The suture stiffens upon cooling. Surface melting of the outer filaments has the effect of holding the filaments together when the suture is cut. It also causes stiffening of the suture which facilitates insertion of the suture end into the drilled hole of a needle. However, the melt fusion of suture has significant drawbacks.
Firstly, the melt fusion of filaments weakens the suture, whose tensile strength is degraded in proportion to the extent of melt fusion.
Secondly, melt fusion causes an irreversible change in the filaments which results in permanent stiffening and permanent loss of tensile strength.
Thirdly, with the temperatures required for melt-fusion an inconveniently short heating cycle is required. For example, for a size 3/0 silicone coated polyester suture heated to between 260.degree. C. to 300.degree. C. in a 4 mm. diameter heating tunnel, the heating time is no more than about 3 seconds. Short heating times allow for more inconsistency and variation in the results of the tipping process than longer heating times.
What is needed is a method for heat tipping sutures which facilitates reversible stiffening of the suture without loss of tensile strength.